In a data transmission system, by adopting a redundant configuration including an active system and a standby system, the reliability of a data transmission can be improved. For example, a data transmission system equipped with a system switching device, a data transmission apparatus including an active system and a standby system, and a data receiving apparatus, has been in practical use. In such data transmission system, when there are no failures in the active system, the system switching device selects the data of the active system of the data transmission apparatus and transmits the data to the data receiving apparatus. When failures occur in the active system of the data transmission apparatus, the system switching device selects the data of the standby system and transmits the data of the standby system to the data receiving apparatus. In this way, even when failures occur in the active system, a data transmission apparatus equipped with an active system and a standby system provides the continuance of communication. As a result, the reliability of the data transmission improves.
As an example related to the art of a communication system having a redundant configuration in a transmission side, a transmission apparatus is disclosed in Japanese Patent Laid-Open No. H08-008886. The transmission apparatus disclosed in Japanese Patent Laid-Open No. H08-008886 prevents the occurrence of loss of frame of a data receiving apparatus when switching a system by synchronizing the frame of the data between an active system and a standby system of a data transmission apparatus.
Furthermore, in a radio base station having a spread processing section of system and system 1, Japanese Patent Laid-Open No. 2002-290314 discloses a configuration of sending a switching control signal to an output control unit of both systems when failures occur in one system.
Further, Japanese Patent Laid-Open No. H10-224430 discloses a composition of a switching system that inhibits any switching operation of a selector depending on an output of switching information.